1. Field of the Invention
The present invention relates to ultrasonic probes, and, more particularly, to trans-esophageal imaging ultrasonic probes.
2. Background of the Invention
Commercial trans-esophageal ultrasonic probes are typically provided with either a bi-plane or multi-plane phased-array transducer mounted at the distal tip. The bi-plane device is based on the integration of two phased-array transducers arranged perpendicular to each other, while the multi-plane device uses a transducer which rotates about an axis parallel to the scanning plane. The flexibility and ease of use thereof makes multi-plane transducers the preferred instrument for use in trans-esophageal examinations in spite of the relatively high cost of these transducers.
The fabrication of phased array multi-plane devices is complicated because of the additional mechanical components required to provide rotation of the transducer array. In order to keep the distal end of the device small for ease of insertion into the esophagus (which is typically 12 to 14 mm across), the rotary drive means for the transducer is typically located, remotely, in the handle of the device. The rotary drive means can be a motor or a manual control handle connected to an associated drive shaft as disclosed, for example, in U.S. Pat. No. 4,543,960. A rotating drive shaft typically transfers the rotary motion from the rotary drive means to the distal tip of the device. This handle also controls the articulation of the distal tip in several planes so as to provide remotely controlled transducer positioning. However, with the rotary drive means located in the housing of the handle, errors can be introduced because of xe2x80x9cwind-upxe2x80x9d in the drive shaft as well as because of a lack of precision associated with the gearboxes or gearing assemblies forming part of the rotary drive means. These sources of error greatly reduce the positional accuracy of the rotating transducer.
Rotating trans-esophageal ultrasound transducers have been developed which incorporate a motor disposed directly in the tip so as to eliminate the inaccuracies discussed above associated with a remotely positioned motor. However, in these transducers, the motor is generally housed in a separate portion of the distal tip from the transducer. Typically, the motor would be housed in a dry chamber and the transducer would be housed in a wet chamber. The wet chamber is filled with an acoustic fluid necessary to provide optimum performance of the transducer. Therefore, rotational seals are required in order to keep the acoustic fluid out of the dry chamber which houses the motor. These seals exert a significant amount of torque on the rotating components that extend through the seals. Because of this increased torque, motors with high torque capabilities are generally required. Integrating such a motor in a miniaturized tip often poses significant problems because high torque motors are generally larger in size than low torque motors.
Rotating trans-esophageal ultrasonic probes are also used for generating three dimensional images. In order to generate a three-dimensional image, multiple images of a two dimensional scan plane must be obtained. Once the two dimensional images are obtained, the images are processed to produce a three dimensional image. For the purposes of trans-esophageal imaging, a longitudinal axis imaging transducer, i.e., a transducer which rotates about the longitudinal axis thereof, is not ideal. Such a transducer is described by U.S. Pat. No. 5,085,221. To use the apparatus in this patent, the physician must first determine the specific region of interest, using standard two dimensional imaging, prior to capturing cardiac images for subsequent three dimensional rendering, and then position the transducer accurately for the three dimensional image capturing. A transverse imaging plane is essential in obtaining this two dimensional information since such an approach can produce a short-axis view of the heart that contains the morphology required for diagnosis. Thus, while a longitudinal image plane device can be utilized to rotate, capture and create a three dimensional rendering, it is difficult to position the device within the esophagus.
In accordance with the invention, an ultrasonic phased array imaging transducer device is provided which overcomes or significantly reduces important problems associated with prior art devices of the same type, including those discussed above.
According to the invention, an ultrasonic phased array imaging transducer device is provided which comprises: a housing having a longitudinal axis, a tip end and a base end; a flexible sealing membrane disposed within said housing and dividing said housing into a wet chamber and a dry chamber; said wet chamber of said housing containing a fluid and including: a phased array transducer disposed in the tip end of said housing, and oriented so as to provide a sound path extending perpendicular to the longitudinal axis of the housing; a motor for rotating the transducer; an encoder for determining positional information with respect to the transducer; a flexible cable electrically connected to said transducer and coiled relative to said transducer so as to permit transducer rotation of more than 180 degrees; and a torque limitation device for limiting torque transmitted to the transducer; said flexible cable extending from the wet chamber through the flexible sealing membrane to the dry chamber.
Preferably, the membrane comprises an elastic member which expands so as to compensate for expansion of the fluid in the wet chamber.
In a preferred implementation, motor includes a drive shaft and the torque limitation device comprises a first gear fixed to the drive shaft of the motor, a second gear directly mounted on the transducer, and a third gear linking the first gear and the second gear so as to provide transmission of rotary drive from the first gear to the second gear. The third gear is preferably arranged so as to provide disengagement of the transmission responsive to torque in excess of a predetermined value being exerted on said transducer. Advantageously, the torque limitation device includes a fourth gear engaging said second gear and mounted on a support shaft, a further gear affixed to the support shaft and a spring for biassing said third gear into engagement with said further gear so that, when said third gear and said further gear are engaged, said third gear provides said transmission and, when said third gear and said further gear are disengaged, said transmission is interrupted.
Preferably, the transducer includes a peripheral gear and the encoder includes an encoder gear engaged with the peripheral gear of said transducer and a mechanical abutment arrangement for providing mechanical limiting of the rotation of the transducer. Advantageously, the encoder includes an encoder disk, and the peripheral gear and the encoder gear have a relative gear reduction ratio permitting rotation of the transducer more than 360xc2x0 with a single said encoder disk.
The motor preferably comprises a means for desynchronizing the motor if a predetermined torque output is exceeded.
Advantageously, the tip and base of said housing have an anatomical shape adapted to fit onto a fingertip of a user. The housing is preferably adapted to be mounted to an endocavity ultrasound probe.
In a preferred implementation, the housing is adapted to be mounted at the distal portion of a laparoscopic probe.
Further features and advantages of the present invention will be set forth in, or apparent from, the detailed description of preferred embodiments thereof which follows.